PSI - Issue 13

M. Khodjet-kesba et al. / Procedia Structural Integrity 13 (2018) 181–186 Author name / Structural Integrity Procedia 00 (2018) 000–000

185

5

The initial conditions being uniform and the boundary conditions are constants, the unidimensional solution of Fick equation can be expressed as (Shen et al. 1981, Khodjet-kesba et al. 2015, 2016):

 

  

2   

2 n D t

(2 1) 

(2 1)

i C C C C  

n z

4 1 1 sin    



 

 

(9)

exp

k

z

2

2 1 n

h

h



 

 

0

n



s

i

Transient and non-uniform moisture concentration has been selected to represent the effect of temperature and moisture in the cracked angle-ply laminates for absorption case. Three sets of environmental conditions are considered. For environmental case 1, Top=22°C and C=0%. For environmental case 2, Top=60°C and C=0.5%. For environmental case 3, Top=120°C and C=1%. The time chosen for simulation is taken equal to tsat=4222h with tsat is the moisture saturation for T300/5208. The characteristics of fibre and matrix of graphite/epoxy (T300/5208) laminate are exposed in Table 2.

Table 2. Fiber and matrix characteristics of graphite/epoxy material (T300/5208) (Tsai 1988). Material properties E fx (Gpa) E fy (Gpa) ν fx E m (Gpa) ν m G m (Gpa)

G fx (Gpa) 19.69

graphite/epoxy (T300/5208)

259

18.69

0.25

3.4

0.35

1.26

The obtained results which are presented in Fig. 4 show that the stiffness is reduced with transverse crack density and fibre angle orientation θ in the outer layers. However, the transient moisture concentration and temperature distribution in absorption case, leads to less reduction of the longitudinal Young’s modulus when the operational temperature and moisture concentration increase for the fibre angle orientation θ less than or equal to 15°. On the other hand, small reduction of the longitudinal Young’s modulus is observed with increasing operational temperature and moisture concentration when the fibre angle θ is greater than 15°. This latter confirmed that the matrix diffusivity in absorption case of the angle-ply laminate depends on the fibre angle orientation, operational temperature and moisture concentration.

1,0

 =0°

0,9

 =15°

0,8

0,7

0,6 Ex (i) /Exo (i) (i=1,2,3)

 =30°

i=1:T=22°C i=2:T=60°C i=3:T=122°C

 =40°

0,5

0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0 0,4

Crack density (1/mm)

Fig.4. Hygrothermal effect on the longitudinal Young’s modulus degradation due to transverse cracks in a [θ/90 3 ] s graphite/epoxy (T300/5208) laminate.

In Fig. 5 the normalized Poisson’s ratio is plotted as a function of crack density with different fibre angles θ°. It has been observed that the Poisson’s ratio reduces monotonically with increased fibre angle θ and also with increase crack density, except for fibre angle θ=0° which gives more accurate reduction of Poisson’s ratio as function of crack density. We note also that the transient hygrothermal effect has significant impact when the fibre angle θ° is small.